Some suggestions along the lines of many above:
- first - get the existing batteries checked by a pro. You can test them yourselves with some research
and intensive setup but easier to get someone else to do it (by putting a known load on each individual batt for a given time and measure volts at start and end). Don't think you are ready for that at the moment. Your also need to determine the age of the batteries and general condition. If wet cells, has the electrolyte ever been below the top of the plates? Outside of the cases - any buldges, cracks, leaks
. Do you just need to replace them right now? Best to replace a set and not just one battery.
- second, figure out exactly what capacity your batteries are - in amp hours.
- third, determine what size (in amps) charger you need for the size of the battery bank you have. Too small and the batts will never get the proper charge even if left on for days. If you need to get the batts recharged in marinas
during a multi-day trip, the batts may never get back up to full and cycle life will drop. Unfortunately the prices of chargers go up rapidly by amps.
fourth - It is entirely OK to get a "pro" to help you with your boat. Not everyone is technically inclined even when motivated with time available. I am not a poet and no amount of research
and practice will make me one. Not everyone will be a good electrician either - despite what a few posters may say. There are good (and bad) pros so get references
and make your own decision as to what a given pro can do for you. If you do feel comfortable getting in to these types of projects then go for it. Just be aware that lots of pros, and other pundits who make come off as pros, often have widely varying advice and may disagree vehemently on any given subject. Battery testing and battery charging are two of those areas unfortunately in some regards, but the basics are fairly simple and well understood. E.g., it is very straightforward to test a start battery but not at all for a deep cycle battery. You might call the battery manufacturer and ask them the best way to test their particular battery. Trojan is particularly helpful. But automotive battery shops will not be much help for deep cycles.
In any case, if you are serious about learning
about your system and what is going on, invest in a good volt/amp meter. One with a clamp-on for measuring AC and DC amps by clamping around a wire. And then learn about electricity - volts, amps, resistance, batteries. And then use it to figure out the volts at the battery charger and at the batteries. Measure the amps coming out of the batteries without charging. Ditto when charging. Check it at the start of charging and hours later. Do it until it all makes sense. If it doesn't make sense you may either not just understand it (yet) or you may have found a problem.